Process and structure to fabricate spin valve heads for ultra-high recording density application

ABSTRACT

A method for forming a bottom spin-valve GMR sensor having ultra-thin layers of high density and smoothness and possessing oxygen surfactant layers as a result of the layers being sputtered in a mixture of Ar and O 2 . A particularly novel feature of the method is the use of a sputtering chamber with an ultra-low base pressure and correspondingly ultra-low pressure mixtures of Ar and O 2  sputtering gas (&lt;0.5 millitorr) in which the admixed oxygen has a partial pressure of less than 5×10 −9  torr.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the fabrication of a giantmagnetoresistive (GMR) magnetic read head, more specifically to the useof an ultra-high vacuum sputtering system to form GMR layers which areinherently furnished with sub-monolayers of adsorbed oxygen (oxygensurfactant layers) for improved deposition properties.

2. Description of the Related Art

Early forms of magnetic read heads decoded magnetically stored data onmedia such as disks and tapes by making use of the anisotropicmagnetoresistive effect (AMR) in magnetic materials such as permalloy.This effect was the change in the electrical resistance, r, of certainmagnetic materials in proportion to the angle between the direction oftheir magnetization and the direction of the current flow through them.Since changing magnetic fields of moving magnetized media, such asmagnetically encoded tapes and disks, will change the direction of themagnetization in a read head, the resistance variations of the AMReffect allows the information on such encoded media to be sensed andinterpreted by appropriate circuitry.

One shortcoming of the AMR effect was the fact that it produced amaximum fractional resistance change, DR/R (where DR is the change inresistance between the magnetic material subjected to its anisotropyfield, H_(k), and the material subjected to zero field), which was onlyon the order of a few percent. This made the sensing process difficultto achieve with accuracy.

In the late 1980's and early 1990's the phenomenon of giantmagnetoresistance (GMR) was discovered and soon applied to read headtechnology. The GMR effect derives from the fact that thin (≅20angstroms) layers of ferromagnetic materials, when separated by eventhinner (≅10 angstroms) layers of conductive but non-magnetic materials,will form ferromagnetic (parallel spin direction of the layers) orantiferromagnetic states (antiparallel spin direction of the layers) bymeans of exchange interactions between the spins. As a result of spindependent electron scattering as electrons crossed the layers, themagnetoresistance of such layered structures was found to besignificantly higher in the antiferromagnetic state than theferromagnetic state and the fractional change in resistance was muchhigher than that found in the AMR of individual magnetic layers.

Shortly thereafter a version of the GMR effect called spin valvemagnetoresistance (SVMR) was discovered and implemented. In the SVMRversion of GMR, two ferromagnetic layers such as CoFe or NiFe areseparated by a spacer layer, which is a thin layer of electricallyconducting but non-magnetic material such as Cu. One of theferromagnetic layers has its magnetization direction fixed in space or“pinned,” by exchange anisotropy with an antiferromagnetic layerdeposited directly upon it. The remaining ferromagnetic layer, theunpinned or free layer, can respond to small variations in externalmagnetic fields such as are produced by moving magnetic media, (which donot affect the magnetization direction of the pinned layer because theexchange pinning strength exceeds the external fields), by rotating itsmagnetization direction. This rotation of one magnetization relative tothe other then produces changes in the magnetoresistance of the threelayer structure which is generally proportional to the cosine of theangle between the magnetization directions.

The spin valve structure has now become the implementation of choice inthe fabrication of magnetic read head assemblies. Differentconfigurations of the spin valve have evolved, including the bottom spinvalve, wherein the pinned layer is at the bottom of the configurationand the top spin valve, wherein the pinned layer is at the top. Inaddition, the qualities of the spin valve have been improved by formingthe pinned layer as a synthetic antiferromagnet, which is a layeredconfiguration comprising two ferromagnetic layers separated by anon-magnetic coupling layer, wherein the ferromagnetic layers aremagnetized in antiparallel directions.

The present challenge to the spin valve form of sensor is to make itsuitable for reading recorded magnetic media with recorded densitiesexceeding 20 Gb/in². This challenge can be met by making the free layerextremely thin, for improved resolution in the track direction, whilenot reducing DR/R, which is a measure of the sensor's sensitivity. Oneway of achieving this goal is by forming the spin valve on a seed layer,which is a layer of material whose purpose is to improve the crystallinestructure of magnetic layers grown upon it. The present inventors havealready shown that spin valves fabricated using a NiFeCr seed layer havea greatly enhanced GMR effect as measured by DR/R. Presently, the NiFeCrseed layer is becoming the industry standard for heads capable ofreading densities exceeding 20 Gb/in². The Cr composition of the seedlayer in these heads is between 20 and 50 atomic percent, with theoptimum value of DR/R obtained with 40 atomic percent. Lee et al. (U.S.Pat. No. 6,141,191) disclose a top spin valve using a NiFeCr seed layerwherein the atomic percentage of Cr is between 20 and 50%. Lee et al.report a DR/R for the configuration of 7.7% which is a significantimprovement over similar sensor formed on Ta seed layers. According toLee et al., the performance improvement is a result of being able to useNiMn as an antiferromagnetic pinning layer, which produces a highpinning field and high blocking temperature.

The present inventors have been using a bottom spin valve configuration(see below) meeting the requirements for reading recorded densitiesgreater than 30 Gb/in², yet its performance would be inadequate forreading area densities of 60 Gb/in²:NiCr(40%)60/MnPt100/CoFe15/Ru7.5/CoFe20/Cu18/OSL/CoFe—NiFe/Ru10/Ta10.In the above configuration the numbers (other than the 40%) refer toapproximate layer thicknesses in angstroms. The NiCr seed layer has 40%atom percent Cr. MnPt is the antiferromagnetic pinning layer,CoFe/Ru/CoFe is a synthetic antiferromagnetic pinned layer, Cu is thespacer layer, OSL represents an oxygen surfactant layer formed on the Cuspacer layer, the surfactant layer being a sub-monolayer of oxygendeposited on the Cu surface by exposing the Cu layer to low-pressureoxygen in a separate chamber, CoFe—NiFe is a composite free layer formedby sequentially sputtering CoFe and NiFe on the surfactant layer andRu/Ta is a composite capping layer wherein the Ru is used to preventinter-diffusion between the Ta and the NiFe.. The configuration providesa DR/R of 12.7% and a sheet resistance, R_(s), of 19.6 ohm/sq.

In order to form sensor structures capable of reading densities inexcess of 60 Gb/in², it is necessary to reduce the track width of thesensor and to reduce the thickness of its free layer, while stillretaining sufficient ratios of DR/R for adequate signal strength.Improvement of DR for a reduced trackwidth sensor can be obtained eitherby increasing sheet resistance of the sensor or DR/R or both. Increasein R_(s) and DR/R can be obtained by thinning the GMR film thickness. Inthis respect, thinning the Cu spacer layer is particularly advantageousbecause it has a very low R_(s). For example, Cu spacer thickness can bereduced from 30 A to 22 A when the Ta seed layer is replaced by theNiFeCr (NiCr) seed layer. For such spin valves, DR/R is increased from6.5% to 9.5%. An NiFeCr (NiCr) seed layer allows the synthetic pinnedlayer upon which the Cu spacer layer is deposited, to be grown with amuch smoother surface, thereby enhancing the spin dependent specularreflectivity of conduction electrons at the inner surface of the Ru/CoFelayers within the synthetic pinned layer. When the surface of the Culayer is treated with oxygen to form an oxygen surfactant layer (OSL),the thickness of the Cu layer can be further reduced to between 22 A and18 A. With an oxygen dose of 10⁻⁴ torr-sec, the surfactant layer is lessthan a mono-layer thick. The formation of the OSL suppresses theinterdiffusion at the Cu/CoFe interface when the CoFe free layer isdeposited on the Cu layer. This increases the spin-dependenttransmission of conduction electrons and suppresses scattering at theinterface. The oxygen is highly mobile and has a strong tendency todiffuse out to the surface of the free layer to improve the specularreflectivity at the GMR outer surface of the CoFe-NiFe/Ru (the surfacebetween the free layer and the capping layer). Because of the highmobility of oxygen in the Cu spacer layer, the oxygen surfactant layercan be formed at a variety of positions within the Cu layer during itsformation. Thus, the surfactant layer can be formed at the Cu bottomsurface where it meets the pinned layer (the CoFe/Cu interface), in themiddle of the Cu layer, or at the Cu/CoFe interface with the free layer.

GMR sensors capable of reading area densities of approximately 45Gb/in², have been made using the following configuration:NiCr(40%)55/MnPt125/CoFe15/Ru7.5/CoFe20/Cu18/SL/CoFe10-NiFe20/Ru10/Ta10.R_(s) of this configuration is approximately 19.5 ohm/sq and DR/R isapproximately 12.8%. Since DR=R_(s)×DR/R, DR=2.5 ohm/sq.

For recording densities greater than 60 Gb/in², DR must be even greater.A practical approach to achieving this increase is to use a thinner freelayer, such as CoFe 5-NiFe 20, together with a thinner layer of MnPt(eg. 100 A), to reduce current shunting through the MnPt. However, thethermal stability of a GMR sensor with these features has been found tobe poor. The GMR configuration has, therefore, used CoFe10/NiFe15 andMnPt 125. In this configuration a DR=2.85 is obtained, which ismarginally adequate for the 60 Gb/in² sensor.

Up to the present time, GMR film stacks have been formed by sputteringin a sputtering system with a base pressure of approximately 10⁻⁸ torr,using Ar as the sputtering gas at a pressure of a few millitorr. This isa typical industry standard for the present generation of sputtered spinvalves. Note in this regard that Sakakima et al. (U.S. Pat. No.6,567,246), who will be discussed further, describes a sputteringprocess (column 16, lines 45–50) with 10⁻⁸ torr base pressure and an Arpressure of 0.8 millitorr.

It is well known that thin film sputtering with an ultra-low sputteringpressure produces a smoother, flatter and denser film. Consequently,under these sputtering conditions, allows a thinner film to be formedwith good qualities. Sputtering with low gas pressure of the sputteringgas (<1 millitorr) requires an ultra-high vacuum system and it isexpected that by coupling the sputtering of GMR layers in such a systemalong with the addition of oxygen to the gas mixture to form asurfactant layer, should allow the formation of very high quality thinfilms. Presently, the design of sputtering systems has improved greatlyand at least one commercially available manufacturing system (the AnelvaC-7100), allows the production of a base pressure of 5×10⁻⁹ torr and anargon sputtering gas pressure as low as 0.1 millitorr. The presentinvention provides a GMR read sensor suitable for recorded densitiesgreater than 100 Gb/in² by making advantageous use of such newsputtering systems. As noted above, Sakakima is utilizing a very highvacuum sputtering system for forming MR elements with oxide magneticfilms such as CoFe₂O₄, wherein such films are in the thickness range ofseveral nanometers, significantly thicker than that envisioned in thepresent invention.

Inoue et al. (U.S. Pat. No. 6,414,825) teach a method for improving thethermal conductivity and hardness of shield gap films by sputtering BN,SiN and CN layers in the presence of oxygen and Ar. In short, there isevidence that the use of Ar and oxygen as sputtering gases can improvethe qualities of a recording medium as well as the film layers in thesensor used to read that medium. Kanbe et al. (U.S. Pat. No. 6,221,508)teaches the use of Ar sputtering with the admixture of small percentagesof other gases (including oxygen at approx. 10%) in forming recordingmedia with reduced grain size for low-noise magnetic recording.

None of the prior art cited teaches the formation of GMR read sensorshaving ultra-thin layers that are rendered smooth by the formation ofoxygen surfactant layers during ultra-low pressure sputtering with Ar asthe sputtering gas and the admixture of a small amount of oxygen.

SUMMARY OF THE INVENTION

A first object of this invention is to provide a method for forming agiant magnetoresistive (GMR) read head sensor element capable of readingrecorded media having densities exceeding 100 Gb/in², along with thegiant magnetoresistive (GMR) sensor element so formed.

A second object of this invention is to provide a method of forming sucha read head in which the layers are smooth and dense and inherentlyfurnished with oxygen surfactant layers at their interfaces.

A third object of this invention is to provide a method of forming sucha read head wherein the oxygen content of the antiferromagnetic pinninglayer is better controlled and is, thereby, provided with improvedexchange coupling properties.

A fourth object of this invention is to provide a method of forming sucha read head wherein a thicker free layer exhibits greater thermalstability during head use.

A fifth object of the present invention is to provide the read headhaving the properties resulting from the formation method hereinafterdescribed.

In accord with the object of this invention there is provided in a firstembodiment a single bottom spin valve sensor element formed bysputtering successive GMR layers on a NiCr seed layer, wherein thesputtering process is carried out at an ultra-low base pressure ofapproximately 5×10⁻⁹ torr using argon admixed with oxygen as asputtering gas at a pressure as low as 0.1 millitorr ( an order ofmagnitude below typical prior art sputtering pressures). The GMRformation process of the present invention utilizes the Ar/O₂ sputteringgases in two different combinations, to obtain two different results.First, every GMR layer, with the exception of the Cu spacer layer andthe Ru capping layer is sputtered by the combined Ar/O₂ gas, preferablyat a total pressure of approximately 0.4 millitorr (within the range of0.1 to 0.6 millitorr). Within this combination, the oxygen is present ata partial pressure of approximately 5×10⁻⁹ torr. This pressure isachieved by combining argon gas from two separate input sources, (1) ahigh purity (99.9995%) argon source which contains less than 0.5 ppm ofO₂ and (2) another source of equally pure argon which is controllablydoped with approximately 500 ppm (between 400 and 600) of O₂. Theadmixed gas contains an oxygen partial pressure of between approximately1× and 10×10⁻⁹ torr. By combining sources (1) and (2) through a mixtureof 25 sccm of (1) and 0.5 sccm of (2), the required 5×10⁻⁹ torr partialpressure O₂ gas mixture is obtained. The sputtering of layers in thiscombined gas produces the dense, smooth layers that are an importantpart of the present invention. Forming the OSL on the Cu layer, however,requires more oxygen than is present in the sputtering mixture, soadditional oxygen must be supplied to form the OSL. This can be done byincreasing the amount of oxygen in the sputtering mixture of the Cuuntil a dose of approximately 10⁻⁴ torr-sec is obtained. Due to themobility of the oxygen in each layer, the oxygen has a tendency to“float” (diffuse) to the surface, effectively producing an OSL on eachsputtered layer. It is noted that the sputtering process time is notlengthened by the admixture of oxygen, because of the small amount ofoxygen that is used.

There is a second and different way of forming an OSL on the Cu spacerand Ru capping layers. In this alternative approach, the sputtering gasfor both the Cu and Ru layers is pure Ar. To produce an OSL on the Cuand Ru layers, the sputtered layers are exposed to O₂ gas in a separatechamber. The O₂ gas is at a pressure of approximately 3×10⁻⁵ torr andthe exposure time is approximately 30 seconds to give a dose ofapproximately 10⁻⁴ torr-sec. It is noted that the OSL on the Ru cappinglayer has the beneficial effect of oxidizing the Ta layer which caps theentire configuration.

The layer configuration of the first embodiment is indicated below:NiCr40/MnPt125/CoFe19/Ru7.5/CoFe20/Cu18/OSL/CoFe10-NiFe20/Ru/TaThis configuration comprises a substrate (not indicated), a 40 angstromthick NiCr seed layer formed on the substrate, a thin (approximately 125angstroms thick) antiferromagnetic MnPt pinning layer which is formed onthe seed layer by sputtering a vacuum melted MnPt target, which has alow oxygen concentration (rather than the usual target made fromsintering, which has a higher oxygen concentration), a syntheticantiferromagnetic (SyAF) pinned layer comprising a CoFe(19)/Ru(7.5)/CoFe(20) tri-layer of the approximate dimensions indicatedin the parentheses above. It is to be noted that the use of vacuummelted MnPt target allows better control of the oxygen content in theMnPt layer, which, in turn, advantageously affects its exchange couplingproperties. A non-magnetic Cu spacer layer, approximately 18 angstromsthick is then formed on the SyAF layer using a different density ofsputtering gases and an oxygen surfactant layer (OSL) is formed on theCu layer. On this OSL, an ultra-thin ferromagnetic free layer is thenformed, said layer being a layer of CoFe of approximate thickness 10angstroms on which is formed a layer of NiFe of approximate thickness 20angstroms.

In a second embodiment there is provided a method of forming aconfiguration that differs from that of the first embodiment by thesubstitution of a NiFeCr—NiFe seed layer, hence:NiFeCr—NiFe/MnPt125/CoFe19/Ru7.5/CoFe20/Cu18/OSL/CoFe10-NiFe20/Ru/Ta

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention areunderstood within the context of the Description of the PreferredEmbodiment, as set forth below. The Description of the PreferredEmbodiment is understood within the context of the accompanying figures,wherein:

FIGS. 1 a–1 c are schematic cross-sectional views of a bottom spin valvesensor element formed in accord with a first second embodiments of themethod of the present invention.

FIG. 2 is a schematic cross-sectional view of a second embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides, in each of two embodiments, a method forfabricating a GMR bottom spin valve sensor element by forming its layersin an ultra-low pressure sputtering system having a base pressure lessthan 10⁻⁸ torr and utilizing ultra low pressure (<0.5 millitorr) Ar/O₂gas as a sputtering gas. The sputtering process produces smooth, denseand thin GMR layers, all of which are inherently provided with oxygensurfactant layers (OSL) as a result of the diffusion of incorporatedoxygen to their surfaces. In addition, the sensor includes a spacerlayer, not formed with the same density sputtering gases, but alsoincorporating an OSL. The sensor element so formed can read recordeddensities exceeding 100 Gb/in².

Experimental Results

Sputtering GMR layers in an ultra-low pressure sputtering environment(eg. the commercially available Anelva device) and using an ultra lowpressure mixture of Ar and O₂ as puttering gases, produces thin filmlayers with the extremely advantageous properties of smoothness and highdensity. In addition, the mobility of the oxygen that becomesincorporated within the layers causes it to diffuse to each layersurface where it forms an oxygen surfactant layer (OSL), which is alsoadvantageous for the laminated layer structure. In the presentexperimental work that led to the determination of the sensor layerconfiguration of the claimed invention, the seed layer on which the GMRsensor layers are formed is sputtered from a NiCr(40%) target and theseed layer is formed to a preferred thickness of approximately 40 A, buta range between approximately 30 and 60 angstroms is acceptable. The useof the O₂ doped Ar as a sputtering gas in the mixtures as discussedabove produces extremely high DR/R for a sensor configuration formed onthe NiCr seed layer. The best DR/R ratios obtained when only Ar is usedas a sputtering gas (as in our prior art depositions) required a seedlayer of NiFeCr(36)/NiFe(8) (thicknesses in angstroms in theparentheses) and the DR/R was less than obtained with the Ar/O₂ mixture.When Ar/O₂ is used to sputter the free layer in the method of thepresent claimed invention, it is found that the incorporated oxygenreduces the magnetic moment of the CoFe by as much as 15%. To maintain aproper magnetic moment, a thicker CoFe layer is required, which isactually advantageous as it improves the thermal stability of the freelayer by more effectively dissipating heat during operation of the head.

The results below indicate various magnetic performance parameters for 7sensor configurations. Configuration (1) is formed in the prior artsputtering system and is provided only for reference purposes.Configurations (2)–(7) represent various seed layers and sputtering gascombinations, all for the low pressure sputtering of the presentinvention. The relevant parameters in all cases are coercive force(H_(c)) of the free layer, for which lower values are advantageous, andDR/R, which, taken together with sheet resistance, R_(s), is a measureof output performance and DR, which is a direct measure of outputamplitude. It is also noted that the pinning field is substantially thesame for all configurations. Finally, it is further noted that the freelayer magnetic moment is slightly reduced in configurations (5)–(7),indicating the effect of the incorporated oxygen. This can be improvedby thickening the free layer, which will also improve its DR/R andthermal stability.

-   (1)    NiCr55/MP125/CoFe19/Ru7.5/CoFe20/Cu18/OSL/CoFe10/NiFe20/Ru10/Ta10    -   Sputter Gas: Ar (2 millitorr for Cu, 5 millitorr for MP (MnPt)        with 38% Mn target)    -   H_(c)=11.06 Oe    -   R_(s)=19.33 ohm/sq    -   DR/R=12.92%    -   DR=2.50 ohm/sq-   (2)    -   NiFeCr36/NiFe9/MP125/CoFe19/Ru7.5/CoFe20/Cu18/OSL/CoFe10/NiFe20/Ru10/Ta10    -   Sputter Gas: Ar (<0.5 millitorr, MnPt sputtered with 38% Mn        target in (3)–(7))    -   H_(c=)5.52 Oe    -   R_(s=)19.10 ohm/sq    -   DR/R=15.06%    -   DR=2.88 ohm/sq-   (3)    -   NiFeCr36/NiFe9/MP125/CoFe19/Ru7.5/CoFe20/Cu18/OSL/CoFe10/NiFe20/Ru5/Ta20    -   Sputter Gas: Ar (<0.5 millitorr)    -   H_(c=)4.76 Oe    -   R_(s=)21.06 ohm/sq    -   DR/R=14.72%    -   DR=3.10 ohm/sq-   (4)    -   NiCr36/NiFe9/MP125/CoFe19/Ru7.5/CoFe20/Cu17/OSL/CoFe10/NiFe20/Ru5/Ta20    -   Sputter Gas: O₂/Ar (<0.5 millitorr, except for Cu and Ru)    -   H_(c=)2.47 Oe    -   R_(s=)21.29 ohm/sq    -   DR/R=15.09%    -   DR=3.21 ohm/sq-   (5)    -   NiCr40/MP125/CoFe19/Ru7.5/CoFe20/Cu17/OSL/CoFe10/NiFe20/Ru5/Ta20    -   Sputter Gas: O₂/Ar (<0.5 millitorr,)    -   H_(c=)8.83 Oe    -   R_(s=)21.78 ohm/sq    -   DR/R=15.79%    -   DR=3.44 ohm/sq-   (6)    -   NiCr40/MP125/CoFe19/Ru7.5/CoFe20/Cu17/OSL/CoFe10/NiFe20/Ru5/Ta20    -   Sputter Gas: O₂/Ar—Ar (<0.5 millitorr, only Ar used to sputter        free layer)    -   H_(c=)7.88 Oe    -   R_(s=)21.21 ohm/sq    -   DR/R=15.83%    -   DR=3.36 ohm/sq-   (7)    -   NiCr40/MP125/CoFe19/Ru7.5/CoFe20/Cu17/OSL/CoFe10/NiFe20/Ru5/Ta20    -   Sputter Gas: O₂/Ar (<0.5 millitorr, MnPt sputtered with 38% Mn        target)    -   H_(c=)10.97 Oe    -   R_(s=)22.87 ohm/sq    -   DR/R=15.79%    -   DR=3.61 ohm/sq        Fabrication of the Preferred Embodiments

Referring first to FIG. 1 a, there is shown a schematic cross-sectionalview of a first portion of a bottom spin valve GMR sensor formed inaccord with the method of the first embodiment of this invention. Whencompleted (FIG. 1 b) it will be substantially the configurationdisclosed as (7) above:NiCr40/MP125/CoFe19/Ru7.5/CoFe20/Cu17/OSL/CoFe10/NiFe20/Ru5/Ta20As previously noted, a novel aspect of the preferred embodiment of theinvention is the sputtering of the GMR sensor layers in an ultra-highvacuum sputtering environment, such as could be obtained in thesputtering chamber of the commercially available Anelva C-7100manufacturing system. The sputtering process is carried out at anultra-low base pressure of approximately 5×10⁻⁹ torr using argon admixedwith oxygen as a sputtering gas within a pressure range between 0.1 and0.6 millitorr, but where 0.4 millitorr is preferable. Within thepreferred embodiment, the oxygen portion of the gas combination ispresent at a partial pressure of approximately 5×10⁻⁹ torr. Thispressure is achieved by combining argon and argon/oxygen gases from twoseparate input sources. Referring to FIG. 1 a, arrows (10) & (20)schematically represent sputtering gases impinging on sputtering targetswhich are not shown in the figure. Arrows (10) represent the gas from ahigh purity (99.9995%) argon source which contains less than 0.5 ppm ofO₂. Arrows (20), represent sputtering gas from another source of equallypure argon which is controllably doped, preferably, with approximately500 ppm (between 400 and 600 being acceptable) of O₂. By combiningsources (10) and (20) through a mixture of approximately 25 sccm of (10)and approximately 0.5 sccm of (20), the required 5×10⁻⁹ torr partialpressure O₂ gas mixture is obtained for sputtering the appropriatetargets.

The sputtering of layers in this combined gas produces the dense, smoothlayers that are an important part of the present invention. Moreover,due to the mobility of the oxygen in each layer, the oxygen has atendency to “float” (diffuse) to the surface, effectively producing anOSL on each sputtered layer. It is noted that the sputtering processtime is not lengthened by the admixture of oxygen, because of the smallamount of oxygen that is used.

In accord with the present method there is first provided a substrate(50). On the substrate there is then formed, by sputtering in theultra-low pressure Ar/O₂ mixture, a seed layer (60) of this invention,which is a layer of NiCr having Cr of approximately 40 atomic percent.The seed layer is formed to a thickness between approximately 35 and 45angstroms, with approximately 40 angstroms being preferred. Upon thisseed layer there is then formed an antiferromagnetic pinning layer (30),which in this embodiment is a layer of MnPt formed to a thickness ofbetween approximately 100 and 150 angstroms but where approximately 125angstroms is preferred. The MnPt layer is sputtered from a vacuum meltedtarget which contains inherently less incorporated oxygen than the moretypical MnPt target formed by a sintered process. The vacuum melt targetis particularly suitable for use with oxygen as one of the sputteringgases as it allows the exercise of more control in producing the oxygencontent of the MnPt layer, which, in turn, is beneficial for itsexchange pinning effects. On the pinning layer there is then formed asynthetic antiferromagnetic (SyAF) pinned layer (70) comprising a firstferromagnetic layer (72) which contacts the pinning layer, on which isformed a non-magnetic antiferromagnetically coupling layer (74), onwhich is formed a second ferromagnetic layer (76). In this embodimentthe first and second ferromagnetic layers are both layers of CoFe, withthe first layer being approximately 19 angstroms thick, with a rangebetween 17 and 21 angstroms being acceptable and the second layer beingapproximately 20 angstroms thick, with a range between 18 and 22angstroms being acceptable. The non-magnetic coupling layer (74) is alayer of Ru approximately 7.5 angstroms thick, with a range between 7and 8 angstroms being acceptable. On the SyAF layer (70) there is thenformed a non-magnetic spacer layer (80), which in this embodiment is aCu layer between approximately 16 and 20 angstroms thick, but whereapproximately 17 angstroms thick is preferred. Unlike the other layersin the sensor, the Cu layer is formed by sputtering only with Ar gas ata pressure of between approximately 0.2 and 0.3 millitorr.

Referring now to FIG. 1 b, there is shown the surface of the Cu spacerlayer (80) not contacting the SyAF layer now treated with additionaloxygen to form an oxygen surfactant layer (OSL), which is shown as abroken line (51). The OSL is less than an atomic mono-layer of oxygenadsorbed on the Cu surface. The OSL formation is most effectively doneby placing the Cu layer surface in contact with low-pressure oxygen (arrows (25)) in a separate oxygen-containing chamber (chamber not shown)at a pressure of approximately 3×10⁻⁵ torr for approximately 30 secondsto obtain a total oxygen dose of approximately 10⁻⁴ torr-sec. The OSLlayer suppresses interdiffusion between the Cu layer and the CoFe layerwhich is about to be formed. This, in turn, enhances the spin-dependenttransmission coefficient for conduction electrons moving through thesensor and across layer interfaces and, correspondingly, suppressesspin-dependent scattering at those interfaces. As previously noted, themobility of the absorbed oxygen would allow the OSL to be formed atdifferent depths in the Cu layer. If, for example, an 18 angstrom thickCu layer is being formed, a first layer of 9 angstroms can be deposited,that layer can then be treated with oxygen, and the remaining 9angstroms of Cu can then be deposited.

Referring now to FIG. 1 c, there is shown the continued deposition onthe OSL surface layer (51), using again the Ar/O₂ mixture in the lowpressure sputtering chamber, a free layer (90), which in this embodimentis a composite layer of CoFe 10/NiFe 15 formed by successive sputteringdepositions. The CoFe (92) is formed to a thickness of betweenapproximately 8 and 12 angstroms, but approximately 10 angstroms ispreferred and the NiFe (94) is formed to a thickness of betweenapproximately 13 and 18 angstroms, but approximately 15 angstroms ispreferred. On the free layer there is finally formed a capping layer.The capping layer is a bilayer comprising a layer of Ru (101) on whichis formed a layer of Ta (102). The Ru layer is formed, using only Ar asthe sputtering gas (as was the case in forming the Cu spacer layer),between approximately 5 and 10 angstroms in thickness, but whereapproximately 5 angstroms is preferred. As noted above, the Ru layer(101) is advantageously given a sub-atomic monolayer OSL (dashed line(111)) in the same manner as the Cu layer (exposure to oxygen in aseparate chamber, as shown for the Cu layer in FIG. 1 b, but which isnot shown again), the OSL layer of the Ru layer producing a beneficialoxidation of the final Ta layer. The Ta layer (102) is formed betweenapproximately 10 and 30 angstroms, but approximately 20 angstroms ispreferred. It is worth noting that the cryo-pump used to pump down thesputtering chamber needs to be regenerated more frequently if the methodis to work at optimal levels.

Referring next to FIG. 2, there is shown a schematic cross-sectionalview of a completely formed bottom spin valve GMR head formed in accordwith the second preferred embodiment of this invention, which isessentially configuration (4) above.NiCr36/NiFe9/MP125/CoFe19/Ru7.5/CoFe20/Cu17/OSL/CoFe10/NiFe20/Ru5/Ta20

All the layers of this embodiment and the OSL are formed exactly as thecorresponding layers of the first preferred embodiment, the soledifference being the seed layer (60), which in this embodiment is alayer of NiFeCr/NiFe, in which the NiFeCr (61) is preferably formed to athickness of approximately 36 angstroms, but wherein a range betweenapproximately 34 and 38 angstroms is acceptable. The NiFe (63) ispreferably formed to a thickness of approximately 9 angstroms, but arange between approximately 7 and 10 angstroms is acceptable. It isnoted that the seed layer of this second embodiment yields superiorexchange properties with the MnPt antiferromagnetic pinning layer.

As is understood by a person skilled in the art, the preferredembodiments of the present invention are illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to materials, structures and dimensionsprovided in forming bottom spin valve GMR sensors capable of readingrecordings with ultra-high densities, while still providing the bottomspin valve GMR sensors capable of reading recordings with ultra-highdensities in accord with the spirit and scope of the present inventionas defined by the appended claims.

1. A method for forming a bottom spin valve GMR sensor element withlayers having sub-atomic monolayers of oxygen absorbed on the surfacesthereof, comprising: providing, in a sputtering chamber having a basepressure, a substrate; forming on said substrate, using an Ar/O₂ mixtureas a sputtering gas, a seed layer; forming, using said sputtering gas,an antiferromagnetic pinning layer on said seed layer; forming, usingsaid sputtering gas, a synthetic antiferromagnetic (SyAF) pinned layerformed on said pinning layer; forming, using only Ar as a sputteringgas, a Cu spacer layer on said SyAF layer, the surface of said spacerlayer not contacting said SyAF layer then being treated with O₂ to forman oxygen surfactant layer (OSL); forming, again using said Ar/O₂mixture, a ferromagnetic free layer on the OSL of said treated spacerlayer; forming, using only Ar as a sputtering gas, a Ru capping layer onsaid ferromagnetic free layer, then forming an OSL layer on said Rulayer; forming, using said Ar/O₂ mixture as a sputtering gas, a Tacapping layer on said Ru capping layer.
 2. The method of claim 1 whereinthe sputtering chamber maintains a base pressure of approximately 5×10⁻⁹torr.
 3. The method of claim 1 wherein said Ar/O₂ mixture is produced bymixing a source of high purity Ar containing oxygen in an amount lessthan 0.5 ppm, with the same Ar source to which between approximately 400and 600 ppm of oxygen has been admixed, said high purity Ar being at anapproximate pressure of 0.4 millitorr and said oxygen having therein apartial pressure of between approximately 10⁻⁹ and 10⁻⁸ torr.
 4. Themethod of claim 1 wherein said antiferromagnetic pinning layer is alayer of MnPt sputtered from a source of vacuum melted MnPt containingapproximately 38% Mn by atomic weight, said layer being formed to athickness between approximately 100 and 150 angstroms.
 5. The method ofclaim 1 wherein the synthetic antiferromagnetic (SyAF) pinned layercomprises a first layer of CoFe between approximately 17 and 21angstroms thick, on which is formed a Ru coupling layer of approximately7.5 angstroms thickness, on which is formed a second layer of CoFebetween approximately 18 and 22 angstroms thick.
 6. The method of claim1 wherein the non-magnetic spacer layer is a layer of Cu betweenapproximately 16 and 20 angstroms thick.
 7. The method of claim 1wherein the OSL is formed by treating the Cu layer with an oxygen doseof approximately 10⁻⁴ torr.-sec in a separate chamber.
 8. The method ofclaim 1 wherein the ferromagnetic free layer is a double layercomprising a layer of CoFe between approximately 8 and 12 angstromsthick on which is formed a layer of NiFe between approximately 13 and 18angstroms thick.
 9. The method of claim 1 wherein the Ru capping layeris formed between approximately 5 and 10 angstroms thick and an OSL isformed thereupon in a separate chamber.
 10. The method of claim 1wherein the Ta capping layer is formed between approximately 10 and 30angstroms thick.
 11. The method of claim 1 wherein said seed layer is alayer of NiCr, having 40% Cr by atomic weight and being formed to athickness between approximately 35 and 45 angstroms.
 12. The method ofclaim 1 wherein said seed layer is a double layer, comprising a layer ofNiFeCr having approximately 40% Cr by atomic weight and of thicknessbetween approximately 35 and 40 angstroms on which is formed a layer ofNiFe of thickness between approximately 7 and 10 angstroms.